PURPOSE: To prevent deformation and melting of a fire grate due to an intensive heat by a method wherein a plurality of fire proofing spherical blocks of A group so as to cover its almost whole area.

CONSTITUTION: Around the lower end of a stove main body 5 a fire grate 6 is provided, and at least one layer of the fire proofing spherical blocks of A group are placed on the fire grate 6 so as to cover fully on it, and further on the spherical blocks of A group B group of oil cokes are dropped into from a dropping port 4. These fire proofing spherical block is to keep their shape and strength constant for a long period, even after contacting with oil cokes in a red heated condition at the time of their combustion, the temperature of which is increased to 1,400°C.